Spark plug



Aug. 23, 1932. 1: G. McDnUGAL SARK PLUG Filed lay 28, 1928 Waw/J JJ//f/V TAINE G. MCDOUGAL, OF FLINT, MICHIGAN,

' 0F lm, HICHIGAN, A

OF MICHIGAN AssiGNoR' To `A c SPARK PLUGCOMPANY,

sranx PLUG Application Med lay 28,

This invention relates to spark plugs for internal combustion engines, and more particularly to an im roveme'nt in the method of assembly and the structure of the center L@ electrode lnan insulator core of quartz.

The use of fused silica or moulded quartz as a spark plug insulator core is highly desirable, princlpally because it is one of the best known non-conductors of electricity at all temperatures, coupled with thefact that it may be heated rapidly or subjected to sudden changes in temperature without liability of fracture or cracking. v

The most remarkable property of quartz is` its low factor of expansion. Quartz has practically no expansion. Since quartz does not expand except to an infinitesimal extent and, whereas the usual metal electrode of a spark plug has a relatively high factor of expansion, considerable trouble hasbeen experenced heretofore in assembling these two different materials, to e'ect and maintain a tight seal so as toavoid leakage of compressed gases. v The present invention contemplates lth provision of an improved type of spark plug unit` comprising a moulded insulator coreI of fused quartz, in which is embedded or formed in situ therein, a portion of a conductor or electrode in a manner to overcome the difliculties encountered in the past with plugs having insulator cores of quartz.`

The invention will be more kfully comprehended upon reference to the accompanying drawing in which:

Figure l is a vertical sectional view of a spark plug embodying the invention; l

Figure 2 is a transverse sectional view on line 2 2 of Figure 1;

Figure 3 is a verticalsectional view of a spark plug showing a modification; and

Figure 4 is a transverse section taken on line 4-4 of Figure 3.

In the drawing, the reference character l indicates an outer metallic shell having a screw threaded portion for engagement within an opening in the engine cylinder and which .surroundsan insulatorcore 2 of fused quartz or similarmaterialkenclosing the center electrode comprising a tip portion 3, an

1928.r B erlal No. 281.205.

intermediate flexible er than the diameter of the central bore in the insulator core 2, and a screw-threaded terminal portion 5 projectingbeyond the top of the core 2, ,for the attachment of a binding nut to connect the electrodewith a currentconducting wire leading from an ignition distributor o 'r similar device.

portion 4 of a size smalli kThemethod of producing the insulator'and l' electrode unit may consistin moulding the fused quartz ,d-irectly'abou't. a portion of the electrode tip 3, which is preferably of conical shape, toinsure a firm embedment, and then inserting thepiiexible portion 4 through the central bore'of the core and electrically welding the'lower end thereof lto the kconical tip 3.y Because of the low' coefficient of` expansion ofthe quartz, the shrinkage of the core upon cooling would not be sufficient to break the tight seal between adjacent portions of the core and electrode tip. Neither will the seal thetendency of the tip to expand and contract upon temperature changes, since thp extent of contact of the parts is sosmall as not to be affected by the total linear'expansion. "The linear expansion of the electrode portions 4 and ,5 relative to the core is compensated for by the flexibility of the portion 4, which allows this intermediate electrode portion to bend to accommodate the extension,` and so prevents the imposition of strains upon'the parts. l

If desired, the electrode tip 3 and portionk4 may be united prior tothe step of moulding the core and, insuch event, the fiexible inter` mediate: portion is preferably coated with some 'suitable material, vsuch as graphite, which will pass away or oxidi ze from the heat of the moulding operation or from heat subse-A quently applied, and so afford clearance for the flexing of the portion 4.

'Ihefsame sort of coating would be applied to the upper portion of the continuous orA one-piececenter electrode 7 shown in themodifedeonstruction of Figure 3. The. mould- .ingl of the core 8 would then result in a tight seal or union at the bottom of the core with the uncoated portion of the electrode and, upon the subsequent removal ofthe graphite be broken by coating, clearance space would be provided for the flexing of the conductor as before referred to.

l claim:

l. The process of making a spark plug unit consisting of coating a portion of an electrode with graphite or the like, and then molding fused quartz or similar insulation around the electrode so as to embed the uncoated portion directly therein and subsequently removing the graphite coating to provide clearance space between adjacent portions of the electrode and insulation.

2. The process described in claim 1,where in the removal of the raphite coating consists of the oxidation 0% the graphite.

3. The process of making a spark plug unit consisting in molding fused quartz or the like about an electrode a portion of which is coated with graphite or its equivalent to directly embed the uncovered portion of the electrode therein.

4. The process of making a spark plug unit consisting of coating a flexible electrode for a portion of its length with graphite, then molding about the electrode a fused quartz core, whereby the uncoated electrode portion is directly embedded in the core and subsequently burning the graphite to provide clearance space in the core in which the unembedded electrode portion is free to flex.

5. The process of making a spark plug unit consisting in molding fused quartz or the like about a central core comprising an exposed metallic electrode portion and a graphite portion to directly embed the exposed portion therein.

6. The process of making a spark plug unit consisting in molding fused quartz or the like about a central core comprising an exposed metallic electrode portion and a graphite portion to directly embed the exposed portion therein, and then removing the graphite portion of the core.

7. The process of making a spark plug unit consisting in molding fused quartz or the like about a central core comprising an fexposed metallic electrode portion and a graphite portion to directl)T embed the exposed portion therein, then removing the graphite portion of the core and inserting in the space from which thegraphite portion has been removed a second electrode portion and securing the same in electric connection relation to the embedded electrode portion.

8. The process of making a spark plug unit consisting of molding fused quartz or the like about a conductor portion to constitute an insulator, inserting a second conductorV portion in the bore formed in the insulator, said second conductor portion being flexible and of smaller diameter than the bore of the insulator, and then molecularly uniting said conductor portions with each other.

9. The process of making a spark plug unit consisting of molding an insulator core of quartz or the like with an electrode tip embedded in the lower end thereof, inserting a flexible conductor throu h the bore of the 

